Problem: $\text C = \left[\begin{array}{rr}-1 & -2 \\ 2 & 2\end{array}\right]$ What is the determinant of $\text C$ ?
Answer: The determinant of a 2x2 matrix can be computed the following way: $ \left|\begin{array}{rr}a & b \\ c & d\end{array}\right| = (a \times d)-(b \times c) $ In this specific case, $ \left|\begin{array}{rr}-1 & -2 \\ 2 & 2\end{array}\right| = (-1 \cdot 2)-(-2 \cdot 2) $ $ = 2 $